Enhanced efficiency of LED structure with n-doped quantum barriers

ABSTRACT

The present invention provides light-emitting devices with improved quantum efficiency. The light emitting diode structure comprising: a p-doped layer, an n-doped layer; and a multiple quantum well structure sandwiched between the p-doped layer and n-doped layer, wherein the multiple quantum well structure comprising a quantum well disposed between n-doped barrier layers.

FIELD OF THE INVENTION

This invention relates to light emitting diodes and more particularly toa microLED with improved quantum efficiency.

BACKGROUND OF THE INVENTION

As a solid-state lighting source with high luminance and a longlifetime, gallium nitride (GaN)/indium gallium nitride (InGaN) microlight emitting diodes (microLEDs) are considered a promising technologyfor many applications, including light sources for optogenetic neuronstimulation, micro-indicators, and self-emissive microdisplays.

The biggest problem restricting the efficiency performance of GaN/InGaNmicroLEDs is efficiency droop. This phenomenon can be mainly attributeddue to factors such as auger recombination, low hole injection, and thecarrier overflow theory. However, surface recombination factor, whichcauses carrier loss, can usually be ignored in GaN/InGaN LEDs.

However, when the size of the microLEDs shrinks down to a fewmicrometers, the surface recombination starts to dominate the efficiencyperformance of GaN/InGaN microLEDs. Almost the entire etching procedurecan severely disrupt the crystal lattice and produce surfacerecombination trap defects. Recombination defects near the surfacedeplete the carriers in this region and draw carriers from thesurrounding regions, causing lateral leakage current and drasticefficiency droop.

Thus, there is a need for an LED structure that can provide improveddevice efficiency performance.

SUMMARY OF THE INVENTION

The present invention provides microLED devices with improved quantumefficiency.

According to one embodiment, microLED structure includes n-doped barrierlayers that provide improved internal quantum efficiency and reducedefficiency droop.

According to another embodiment, the microLED structure may comprises asingle quantum well disposed between the n-doped barrier layers.

According to one embodiment, a light emitting diode structure may beprovided. The light emitting diode structure may comprising a p-dopedlayer, an n-doped layer, and an active zone between the p-doped layerand n-doped layer, the active zone comprising a multiple quantum wellstructure, wherein the multiple quantum well structure comprising aquantum well disposed between n-doped barrier layers.

According to yet another embodiment, a light emitting diode structuremay be provided. The light emitting diode structure may comprising asubstrate, an n-doped layer deposited on the substrate, an active zonegrown over the n-doped layer, the active zone comprising a multiplequantum well structure, wherein the multiple quantum well structurecomprising a quantum well disposed between n-doped barrier layers, anelectron blocking layer deposited on the active zone; and a p-dopedlayer deposited on the electron blocking layer.

According to some embodiments, an optimized design for 5×5 μm² microLEDswith n-doped barrier layers and a single quantum well shows anefficiency improvement of 128% at a current density of 20 A/cm² ascompared to a conventional design with intrinsic multiple quantum wellactive regions.

According to one embodiment, the n-doped barrier layers flatten theconduction band and reduce the current leakage from n-GaN layer to p-GaNlayers.

According to another embodiment, the Shockley-Read-Hall (SRH)recombination rate in a light-emitting device with n-doped barrierlayers is much smaller than the SRH recombination rate in alight-emitting device with p-doped barrier layers. Thus, n-doped QWbarriers performs better than devices with undoped or p-doped QWbarriers in small dimensions (less than 10 um).

The foregoing and additional aspects and embodiments of the presentdisclosure will be apparent to those of ordinary skill in the art inview of the detailed description of various embodiments and/or aspects,which are made with reference to the drawings, a brief description ofwhich is provided next.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other advantages of the disclosure will becomeapparent upon reading the following detailed description and uponreference to the drawings.

FIG. 1A shows a cross-sectional view of an LED structure having multiplequantum wells and p-doped barrier layers, in accordance with anembodiment of the invention.

FIG. 1B shows a cross-sectional view of an LED structure having a singlequantum well disposed between n-doped barrier layers, in accordance withan embodiment of the invention.

FIG. 2A is a graph of internal quantum efficiency (IQE) versus currentdensity of an InGaN/GaN based LED, in accordance with an embodiment ofthe invention.

FIG. 2B depicts an I-V curve characterizing voltage versus currentdensity of an InGaN/GaN based LED, in accordance with an embodiment ofthe invention.

FIG. 3 is a graph of the measured relative external quantum efficiency(EQE) at different temperatures of an InGaN/GaN based LED, in accordancewith an embodiment of the invention.

FIGS. 4A-4D depict graphs comparing IQE against current density forGaN/InGaN micro light-emitting diodes with different dimensions anddifferent doping profiles of quantum well barriers, in accordance withan embodiment of the invention.

FIG. 5 is a graph comparing IQE against current density for InGaN/GaNmicro light-emitting diodes with different doping concentrations ofn-type quantum well barriers, in accordance with an embodiment of theinvention.

FIG. 6A is an energy band diagram of the p-doped barrier layers of theLED structure shown in FIG. 1A, in accordance with an embodiment of theinvention.

FIG. 6B is an energy band diagram of the n-doped barrier layers of theInGaN/GaN based LED structure shown in FIG. 1B, in accordance with anembodiment of the invention.

FIG. 7 is a graph comparing IQE against current density between anoptimized microLED and a conventional microLED, in accordance with anembodiment of the invention.

Use of the same reference numbers in different figures indicates similaror identical elements.

While the present disclosure is susceptible to various modifications andalternative forms, specific embodiments or implementations have beenshown by way of example in the drawings and will be described in detailherein. It should be understood, however, that the disclosure is notintended to be limited to the particular forms disclosed. Rather, thedisclosure covers all modifications, equivalents, and alternativesfalling within the spirit of the invention as defined by the appendedclaims.

DETAILED DESCRIPTION

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs.

As used in the specification and claims, the singular forms “a,” “an”and “the” include plural references unless the context clearly dictatesotherwise.

The term “comprising” as used herein will be understood to mean that thelist following is non-exhaustive and may or may not include any otheradditional suitable items, for example one or more further feature(s),component(s) and/or element(s) as appropriate.

The terms “device” and “micro device” are used herein interchangeably.It would be clear to one skill in the art that the embodiments describedhere are independent of the device size.

In this disclosure, InGaN/GaN based LEDs are used as an example,However, the simulations result may applicable to other LED structuresbased on different material systems, such as GaAsP based LEDs, InGaAsPbased LEDs, InGaAs based LEDs, or GaAs based LEDs.

The multiple quantum well structure may comprise quantum well andbarrier layers. The quantum well may comprise one of: GaAs, InGaN,InGaAs, AlGaN and InGaAsP and the barrier layers may comprises one of:AlGaAs, GaN, AlGaAs, AlGaN and InP.

This disclosure provides a design of microLED structure using a singlequantum well disposed between n-doped barrier layers to improve theefficiency performance, contrary to LEDs with regular sizes (i.e.,greater than 100 μm) in which the barrier layers are typically p-dopedto improve device efficiency performance.

According to one aspect of the invention, an optimized design for 5×5μm² microLEDs with n-doped barrier layers and a single quantum wellshows more than 100% efficiency improvement at a current density of 20A/cm² compared to a conventional intrinsic multiple quantum well baseddesign.

In conventional quantum well structures, a surface recombinationvelocity in GaN and InGaN is typically around 1×10² cm/s to 1×10⁵ cm/sand the surface recombination area is around 1 μm from the semiconductorsurface.

According to another aspect of the invention, Apsys software is employedto simulate GaN/InGaN based microLEDs by setting a surface recombinationrange of 1 μm and surface recombination velocity of 3×10⁴ cm/s.

In one case, temperature-dependent measurements for the 50×50 μm²microLEDs are set to check the reliability of the simulation results.

Conventional p-i-n Structure with p-Doped Quantum Well Barrier Layers

FIG. 1A shows a cross-sectional view of a typical MQW heterostructure ofan InGaN/GaN based LED. The heterostructure may comprise a growthsubstrate 102 (e.g., sapphire), an n-type GaN layer 104 formed on thesubstrate 102, a MQW structure 120 grown on the n-type GaN layer togenerate radiation, an electron blocking layer 108, and a p-type GaNlayer 110. The MQW structure 120 may comprise a plurality of alternatingbarrier layers 124 and quantum wells 122 (for example, six pairs ofalternating quantum wells 122 sandwiched by barrier layers 124). In oneexample, the quantum wells 122 may comprise InGaN and the barrier layers124 may comprise p-doped GaN.

The electron blocking layer 108 can be deposited on the MQW structure120. In one case, the electron blocking layer may comprise p-type dopedAlGaN. Then, a p-type GaN layer may be deposited on the p-type AlGaN.Further, a p-type metal contact 112 such as Pd/Au, Pt or Ni/Au is formedon the p-type GaN layer. Also, the substrate (e.g., sapphire) is aninsulator, and the n-type GaN layer 104 is exposed to make contact tothis layer. This step is usually done using a dry-etch process to exposethe n-type GaN layer and then deposit the appropriate metal contacts(e.g., n-type metal contact 106).

The conventional p-doped barrier layers are well suited for GaN/InGaNLEDs with a regular size (>100 μm in dimension) to improve deviceefficiency performance.

However, when the size of microLEDs shrink down to a few micrometers(e.g., 5×5 μm²), the surface recombination starts to dominate theefficiency performance of GaN/InGaN p-doped barriers layers.

LED Structure with n-Doped Quantum Well Barrier Layers

FIG. 1B shows cross-sectional view of an InGaN/GaN based LED with asingle quantum well disposed between n-doped barrier layers, inaccordance with an embodiment of the invention. The light-emittingdevice according to the present embodiment may comprise a growthsubstrate 102 (e.g., sapphire), an n-type GaN layer 104 formed on thesubstrate, a MQW active zone 120 grown on the n-type GaN layer togenerate radiation, an electron blocking layer 108, and a p-type GaNlayer 110.

Here, the MQW structure 120 may comprise a single quantum well 222disposed between n-doped barrier layers 224. In one example, the quantumwell 222 may comprise InGaN and the barrier layers 224 may comprisen-doped GaN. However, the simulations result may applicable to other LEDstructures based on different material systems, such as GaAsP basedLEDs, InGaAsP based LEDs, InGaAs based LEDs, or GaAs based LEDs. Thequantum well may comprise one of: GaAs, InGaN, InGaAs, AlGaN and InGaAsPand the barrier layers may comprises one of: AlGaAs, GaN, AlGaAs, AlGaNand InP.

According to one aspect of the invention, compared to the MQW structureshown in FIG. 1A, the single quantum well structure shown in FIG. 1B mayreduce the ratio of surface area to volume, alleviate the surfacerecombination problems and significantly improve quantum efficiency.

Experimental and Simulation Results Analysis of GaN/InGaN Light-EmittingDiodes with p-Doped Barrier Layers

Here, InGaN/GaN based LEDs are used as an example, However, thesimulations result may applicable to other LEDs based on differentmaterial systems.

By setting the surface recombination range and the surface recombinationvelocity, the current-voltage curve and device quantum efficiency of a50×50 μm² GaN/InGaN microLED were simulated at different temperatures,which are in good agreement with experimental results.

Simulations of the internal quantum efficiency of the LED structure ofFIG. 1A are carried out with the Apsys software by setting the surfacerecombination velocity in GaN and InGaN to typically around 1×10² cm/sto 1×10⁵ cm/s, the surface recombination velocity to 3×10⁴ cm/s, and thesurface recombination area to around 1 μm from the semiconductor surfaceas described below.

FIG. 2A is a graph of internal quantum efficiency (IQE) versus currentdensity of a InGaN/GaN based LED, in accordance with an embodiment ofthe invention. The graph shows simulation and experimental results at atemperature of 300K on a log scale. Here, the LEDs are 50×50 μm² insize. In one case, the curve shows that the efficiency peak of thedevice shifts to a lower current density. The simulation results fit theexperimental results well at room temperature. The differences shownbetween the simulation and experimental results because the microLEDs insimulation results cannot reflect the indium clustering issue in thequantum wells of actual (experimental) devices. The LEDs with nonuniformindium composition in quantum wells have a lower performance.

FIG. 2B depicts an I-V curve characterizing voltage versus currentdensity of an InGaN/GaN based LED on a log scale, in accordance with anembodiment of the invention. The current density range of experimentalresults is from 0.4 to 20 A/cm². As seen in the graph, with larger size(50×50 μm²), devices with p-doped barrier layers exhibit betterperformance in most of the common operation current density range (1A/cm² to 50 A/cm²).

In one case, to verify the simulation, temperature-dependent measurementby experiment and simulation can be done.

FIG. 3 is a graph of the measured relative external quantum efficiency(EQE) at different temperatures of an InGaN/GaN based LED, in accordancewith an embodiment of the invention. The graph shows that the EQE almostdoubles when the temperature decreases from 300K to 140K.

This increase in EQE occurs because low temperatures suppress thenon-radiative recombination in the active region of the LED. However,when the temperature furtherly decreases below 120K, the EQE stronglydecreases. The first reason for a decrease in efficiency at lowtemperatures is mainly due to the fluctuation in the quantum wells. Theelectroluminescence spectrum of InGaN/GaN LEDs first shifts to blue andthen shifts to red between 300K to 5K. The energy peak positiondifference can be up to 40 meV. The imbalanced spatial distribution ofindium (In) also reduces the density of radiative recombination centersin quantum wells. The quantum wells tend to cluster in a two to threenanometer region, with less radiative recombination centers in otherregions. Some injected carriers overflow and reduce carrier injectionefficiency, and even lower temperatures can aggravate this problem.

The second reason that InGaN/GaN-based LEDs exhibit poor performance inlow temperature situations is the high activation energy or presence ofMg in GaN. Due to the high activation energy of the acceptors of GaN,the hole concentration dramatically decreases, and the recombinationzone shifts from the active region to the p-type GaN region at lowtemperature, which leads to lower efficiency.

The differences between experimental and simulation results in FIG. 3occur because the simulated LEDs cannot reflect the indium clusteringissue in the quantum wells of actual devices. The nonuniform indium (In)spatial distribution leads the nonuniform radiative carrier lifetimeτ_(rad), which averages the total τ_(rad) in quantum wells and smoothsthe curves. Therefore, the simulated temperature-dependent efficiencygraph in FIG. 3 has a dramatic efficiency droop at around 90K, which islower than the experimental one (around 120K) while the slope is larger.

Therefore, a more optimized LED design that can improve efficiencyperformance is needed.

Further, the simulation results can be discussed as follows.Theoretically, the internal quantum efficiency (IQE) of GaN/InGaN LEDscan be described by a simple model equation:

$\begin{matrix}{\eta_{IQE} = \frac{\eta_{inj}{BN}^{2}}{{AN} + {BN}^{2} + {CN}^{3}}} & (1)\end{matrix}$where η_(inj) is the injection current efficiency, N is the carrierdensity in quantum wells, and A, B, C, are the Shockley-Read-Hall (SRH)nonradiative recombination coefficient, the radiative coefficient, andthe Auger coefficient, respectively. The peak efficiency η_(peak) can beinferred when dη_(IQE)/dN=0, and the carrier density at peak efficiencycan be obtained as N_(peak)=√{square root over (AC)} using equation (1).

For microLEDs that are just a few micrometers, the surface recombinationoverwhelms the auger recombination and dominates the nonradiativerecombination. This means that the N_(peak) shifts to a very high valueand crosses the regular current operating range of an LED (i.e., greaterthan 100 A/cm²). This phenomenon illustrates that GaN/InGaN microLEDswith a smaller dimension no longer suffer from efficiency droop, butinstead efficiency slowly rises with the injection current.

On the other hand, by neglecting the auger term, equation (1) with a lowinjection level can be simplified to:

$\begin{matrix}{\eta_{IQE} = {\eta_{inj}\frac{1}{\frac{A}{BN} + 1}}} & (2)\end{matrix}$

As seen in equation (2), increasing the carrier density N in quantumwells improves η_(IQE). In one case, doping the barrier layers of an MQWactive region can increase the carrier density in quantum wells. Theadditional electrons or holes compensate the carriers of the microLEDsfor radiative recombination lost in current leakage due to nonradiativesurface recombination.

Accordingly, p-doped barrier layers are commonly applied to alleviatethe efficiency droop problem of GaN/InGaN LEDs caused by the low holeinjection issues in GaN/InGaN LEDs.

Simulation and Experimental Analysis of GaN/InGaN Micro Light-EmittingDiodes with n-Doped Quantum Well Barriers

FIGS. 4A-4D depict graphs comparing IQE against current density forGaN/InGaN LEDs with different dimensions and different doping profilesof barrier layers, in accordance with an embodiment of the invention.

Here, as an example, simulated IQE results of LEDs with differentdimensions (i.e, 100×100 μm², 50×50 μm², 10×10 μm², and 5×5 μm²) andbarrier layers with different doping profiles (i.e., intrinsic, p-dopedat 1×10¹⁷ cm⁻³, and n-doped at 1×10¹⁷ cm⁻³) at room temperature areshown. These results show that the IQE value significantly deterioratesas the device size shrinks to 5×5 μm², and is strongly affected by thedoping profile.

FIG. 4A shows a graph of IQE versus current density for 100×100 μm²GaN/InGaN LEDs. Here, the microLEDs have the dimensions 100×100 μm². Thegraph shows a comparison between different doping profiles of barrierlayers. The doping profiles may comprise intrinsic active regions,p-doped active regions at 1×10¹⁷ cm⁻³, and n-doped active regions at1×10¹⁷ cm⁻³. As seen from the graph, larger size (100×100 μm²) deviceswith p-doped barrier layers exhibit better performance in most of thecommon operation current density ranges (i.e., 1 A/cm² to 50 A/cm²)compared to intrinsic active regions and n-doped active regions.

FIG. 4B shows a graph of IQE versus current density for a 50×50 μm²GaN/InGaN LED. The graph shows a comparison between different dopingprofiles of barrier layers. The doping profiles may comprise intrinsicactive regions, p-doped active regions at 1×10¹⁷ cm⁻³, and n-dopedactive regions at 1×1×10¹⁷ cm⁻³. As seen from the graph, even when thedevice size shrinks to 50×50 μm², devices with p-doped barrier layersexhibit better performance in most of the common operation currentdensity ranges (i.e., 1 A/cm² to 50 A/cm²) compared to intrinsic activeregions and n-doped active regions.

FIG. 4C shows a graph of IQE versus current density for 10×10 μm²GaN/InGaN microLEDs. The graph shows a comparison between differentdoping profiles of barrier layers. The doping profile may compriseintrinsic, p-doped at 1×10¹⁷ cm⁻³, and n-doped at 1×10¹⁷ cm⁻³. As seenfrom the graph, when the device size further shrinks to 10×10 μm²,devices with n-doped barrier layers start performing better.

Here, the Shockley-Read-Hall (SRH) recombination mechanism can beanalyzed. The SRH recombination rate is given through the SRH formula:

$\begin{matrix}{R_{SRH} = \frac{{np} - n_{i}^{2}}{{\tau_{p}\frac{n}{f_{n}}} + {\tau_{n}\frac{p}{I - f_{p}}}}} & (3)\end{matrix}$where τ_(p,n) is the SRH lifetime and f_(n′p) is the trap occupationprobabilities.

With the same doping concentration, the SRH recombination rates at smallinjection levels in a GaN/InGaN LED with p-doped or n-doped barrierlayers are:

$\begin{matrix}{R_{SRH}^{n} \equiv \frac{\Delta\;{np}_{0}f_{n}}{\tau_{p}( {n_{0} + {\Delta\; n}} )}} & (4) \\{R_{SRH}^{p} \equiv \frac{\Delta\;{{pn}_{0}( {1 - f_{p}} )}}{\tau_{n}( {p_{0} + {\Delta\; p}} )}} & (5)\end{matrix}$

where the trap occupation probabilities f_(n) in equation (4) and1−f_(p) in equation (5) probably equal each other.

The proportional magnitude between τ_(p) and τ_(n) can be considered asthe proportional magnitude between the hole and electron lifetime,τ_(p0) and τ_(n0), respectively. In GaN, τ_(p0) is much larger thanτ_(n0). Therefore, the SRH recombination rate R^(n) _(SRH) in a devicewith n-doped barrier layers is much smaller than the SRH recombinationrate R^(p) _(SRH) in a device with p-doped barrier layers.

FIG. 4D shows a graph of IQE versus current density for 5×5 μm²GaN/InGaN microLEDs. The graph shows a comparison between differentdoping profiles of barrier layers. The doping profile may compriseintrinsic, p-doped at 1×10¹⁷ cm⁻³, and n-doped at 1×10¹⁷ cm⁻³. As seenfrom the graph, when the devices shrink to 5×5 μm², devices with n-dopedbarrier layers perform better than devices with undoped or p-dopedbarrier layers in small dimensions (i.e., less than 10 μm).

Although n-doped barrier layers can improve the efficiency of GaN/InGaNLEDs, n-doped barrier layers can aggravate the low hole injectionproblem and push the recombination zone close to the p-type GaN region.

Therefore, a very high doping concentration of n-doped barrier layershas a very strong efficiency droop problem and weakens the efficiencyperformance.

According to one aspect, revising the doping concentration in n-dopedbarrier layers shows the best performance of the simulated 5×5 μm²microLEDs by balancing the low holes injection and high nonradiative SRHrecombination rate problems.

FIG. 5 is a graph comparing IQE versus current density for GaN/InGaNmicroLEDs with different n-type doping concentrations of barrier layers,in accordance with an embodiment of the invention. Here, the microLEDsare 5×5 μm² and exhibit different efficiency curves based on differentn-type doping concentrations. For example, the doping concentrations are5×10¹⁷ cm⁻³, 1×10¹⁷ cm⁻³, and 1×10¹⁸ cm⁻³ as shown in the graph. Amongsix sets of n-doped barrier layers with different doping concentrations,the 5×10¹⁷ cm⁻³ n-doped quantum well barriers is the most optimizeddesign.

FIG. 6A is an energy band diagram of the p-doped barrier layers of theInGaN/GaN based LED structure as shown in FIG. 1A. Theoretically, an LEDemits energy corresponding to an energy gap of a conduction band and avalance band by combining electrons of an n layer and holes of a p layerupon applying a forward voltage.

The energy band diagram of the LED structure with p-doped barrier layershas been shown in FIG. 6A. As seen in the graph, the conductive band ofMQW is not flat and there is current leakage from the n-GaN to p-GaNlayers.

FIG. 6B is an energy band diagram of the n-doped barrier layers of theInGaN/GaN based LED structure shown in FIG. 1B. The energy band diagramof the LED structure is shown with n-doped barrier layers. As seen inthe graph, n-doped barrier layers flatten the conductive band and reducethe current leakage from n-GaN to p-GaN layers.

From the energy band diagrams discussed above, the n-doped barrierlayers surpasses the current leakage factor and improve efficiencyperformance.

FIG. 7 is a graph comparing IQE against current density between anoptimized microLED and a conventional LED, in accordance with anembodiment of the invention. The graph shows an efficiency performancecomparison of 5×5 μm² microLEDs with a single quantum well and n-dopedbarrier layers with a conventional LED structure. The conventionalstructure may have MQWs with intrinsic quantum well barrier layers.Compared to the MQW design, a single quantum well LED structure reducesthe ratio of surface area to volume and alleviates the surfacerecombination problems. The graph reveals that the optimized LED designcan achieve a 128% IQE improvement at 20 A/cm² compared to aconventional design with intrinsic MQW active regions.

According to one embodiment, a light emitting diode structure may beprovided. The light emitting diode structure may comprising a p-dopedlayer, an n-doped layer, and an active zone between the p-doped layerand n-doped layer, the active zone comprising a multiple quantum wellstructure, wherein the multiple quantum well structure comprising aquantum well disposed between n-doped barrier layers.

According to another embodiment, the quantum well may comprise one of:GaAs. InGaN, InGaAs, AlGaN and InGaAsP and the barrier layers maycomprises one of: AlGaAs, GaN, AlGaAs, AlGaN and InP. The n-dopedbarrier layers has a flat conduction band and reduced current leakagefrom n-doped layer to p doped layer.

According to yet another embodiment, each of the barrier layers may bedoped with a dopant concentration ranging from undoped to 1×10¹⁸ cm⁻³Each of the barrier layers may be doped with a dopant concentration of5×10¹⁷ cm⁻³. The barrier layers may have a current density in a range of0 to 50 A/cm². The barrier layers may have a current density of 20A/cm².

According to some embodiments, the light emitting diode structure mayfurther comprising: a substrate, wherein the n-type doped layer isdeposited on the substrate and the multiple quantum well structure isgrown over the n-type doped layer; and an electron blocking layerdeposited on the multiple quantum well structure, wherein the p-typedoped layer is deposited on the electron blocking layer.

According to one embodiment, the light emitting diode structure mayfurther comprising: a p-type contact and an n-type contact deposited onthe light emitting diode structure. The n-doped layer comprises ann-type GaN layer. The p-doped layer comprises a p-type GaN layer.

According to yet another embodiment, a light emitting diode structuremay be provided. The light emitting diode structure may comprising asubstrate, an n-doped layer deposited on the substrate, an active zonegrown over the n-doped layer, the active zone comprising a multiplequantum well structure, wherein the multiple quantum well structurecomprising a quantum well disposed between n-doped barrier layers, anelectron blocking layer deposited on the active zone; and a p-dopedlayer deposited on the electron blocking layer.

According to some embodiments, the multiple quantum well structurecomprises one of: GaAs/AlGaAs, InG InaN/GaN, InGaAs/AlGaAs, AlGaN/AlGaNand InGaAsP/InP.

According to one embodiment, a method of manufacturing a light emittingdiode structure may be provided. The method may comprising providing asubstrate, forming an n-doped layer on the substrate; and forming amultiple quantum well structure over the n-doped layer, wherein themultiple quantum well structure comprising a quantum well disposedbetween n-doped barrier layers.

According to another embodiment, the method may further comprisingforming an electron blocking layer on the multiple quantum wellstructure; and forming a p-type doped layer on the electron blockinglayer.

According to yet another embodiment, the substrate may comprises asapphire substrate. Each of the barrier layers may be doped with adopant concentration ranging from undoped to 1×1018 cm−3. each of thebarrier layers may be doped with a dopant concentration of 5×1017 cm−3.The barrier layers may have a current density in a range of 0 to 50A/cm2. The barrier layers may have a current density of 20 A/cm2.

In summary, an optimized design for 5×5 μm² microLEDs with n-dopedbarrier layers and a single quantum well shows an efficiency improvementof 128% at a current density of 20 A/cm² as compared to a conventionaldesign with intrinsic MQW active regions.

The foregoing description of one or more embodiments of the inventionhas been presented for illustration and description purposes. It is notintended to be exhaustive or to limit the invention to the precise formdisclosed. Many modifications and variations are possible in light ofthe teaching herein. The scope of the invention is not intended to belimited by this detailed description, but rather by the appended claims.

The invention claimed is:
 1. A light emitting diode structurecomprising: a p-doped layer; an n-doped layer; and a multiple quantumwell structure sandwiched between the p-doped layer and n-doped layer,the multiple quantum well structure comprising: a quantum well disposedbetween n-doped barrier layers.
 2. The light emitting diode structure ofclaim 1, wherein the quantum well comprises one of: GaAs, InGaN, InGaAs,AlGaN and InGaAsP.
 3. The light emitting diode structure of claim 1,wherein the barrier layers comprise one of: AlGaAs, GaN, AlGaAs, AlGaNand InP.
 4. The light emitting diode structure of claim 1, wherein then-doped barrier layers have a flat conduction band and reduced currentleakage from n-doped layer to p-doped layer.
 5. The light emitting diodestructure of claim 1, wherein each of the barrier layers is doped with adopant concentration ranging from undoped to 1×10¹⁸ cm⁻³.
 6. The lightemitting diode structure of claim 5, wherein each of the barrier layersis doped with a dopant concentration of 5×10¹⁷ cm⁻³.
 7. The lightemitting diode structure of claim 1, wherein the barrier layers have acurrent density in a range of 0 to 50 A/cm.
 8. The light emitting diodestructure of claim 7, wherein the barrier layers have a current densityof 20 A/cm².
 9. The light emitting diode structure of claim 1, furthercomprising: a substrate, wherein the n-type doped layer is deposited onthe substrate and the multiple quantum well structure is grown over then-type doped layer; and an electron blocking layer deposited on themultiple quantum well structure, wherein the p-type doped layer isdeposited on the electron blocking layer.
 10. The light emitting diodestructure of claim 1, further comprising: a p-type contact and an n-typecontact deposited on the light emitting diode structure.
 11. The lightemitting diode structure of claim 1, wherein the n-doped layer comprisesan n-type GaN layer.
 12. The light emitting diode structure of claim 1,wherein the p-doped layer comprises a p-type GaN layer.
 13. A lightemitting diode structure comprising: a substrate; an n-doped layerdeposited on the substrate; a multiple quantum well structure formedover the n-doped layer, wherein the multiple quantum well structurecomprising a quantum well disposed between n-doped barrier layers; anelectron blocking layer deposited on the multiple quantum wellstructure; and a p-doped layer deposited on the electron blocking layer.14. The light emitting diode structure of claim 13, wherein the quantumwell comprises one of: GaAs, InGaN, InGaAs, AlGaN and InGaAsP.
 15. Thelight emitting diode structure of claim 13, wherein the barrier layerscomprise one of: AlGaAs, GaN, AlGaAs, AlGaN and InP.
 16. A method ofmanufacturing a light emitting diode structure, the method comprising:providing a substrate; forming an n-doped layer on the substrate; andforming a multiple quantum well structure over the n-doped layer,wherein the multiple quantum well structure comprising a quantum welldisposed between n-doped barrier layers.
 17. The method of claim 16,further comprising forming an electron blocking layer on the multiplequantum well structure; and forming a p-type doped layer on the electronblocking layer.
 18. The method of claim 16, wherein the substratecomprises a sapphire substrate.
 19. The method of claim 16, wherein eachof the barrier layers is doped with a dopant concentration ranging fromundoped to 1×10¹⁸ cm⁻³.
 20. The method of claim 16, wherein the barrierlayers have a current density in a range of 0 to 50 A/cm².